This invention relates generally to an adjustment control system for a grain cleaning sieve or sieves of an agricultural combine, and more particularly, to a method of automatic operation of a sieve control system for adjusting the sieve opening size or position while mitigating error and inaccuracy resulting from tolerance stack-up of mechanical components in the system.
It is well known to provide an automatic system for adjusting the sieve or sieves of the grain cleaning system of an agricultural combine. Typically, the cleaning system will consist of two sieves, an upper or coarser sieve or chaffer located below the threshing mechanism or separator of the combine and having larger sieve openings for the passage of grain and smaller pieces of plant material therethrough but relatively little of the larger chaff, and a lower finer sieve located below the chaffer for receiving the grain and smaller pieces of plant material therefrom and having smaller sieve openings for passage of the grain therethrough but relatively little of the plant material. The collected and cleaned grain, once through the sieves is then typically transported by conveyor or other means to a clean grain bin on the combine, or to an accompanying grain receiving vehicle. The opening sizes of the chaffer and sieve are an important parameters for controlling the amount or yield of grain that is recovered by the combine as opposed to discharged therefrom with the chaff and other unwanted plant material and crop residue. Accordingly, the chaffer and sieve opening sizes are typically set at the commencement of the harvesting operation, and may be reset at times during the harvesting operation, to achieve a desired crop yield rate.
A typical sieve construction includes a plurality of elongate parallel, pivotally mounted slats, each slat including a plurality of longitudinally spaced upwardly extending inclined fingers, the slats being pivotable through a range of open positions angularly oriented to horizontal for providing a corresponding range of openings or spaces between the fingers of adjacent ones of the slats. A typical automatic sieve adjusting system includes an adjusting member which contacts each of the slats, and a linkage and/or cable arrangement connected between the adjusting member and one or more actuators driven by an electrical, fluid, or other controller for moving the linkage or cable arrangement and member and thus changing the angular orientation of the slats and as a result, the opening size. The typical controller includes at least one processor operated by stored commands and/or inputs for controlling an electrical drive motor or the like for moving the actuator. An input device such as a push button or keypad and a display device are typically located in the operator cab of the combine for changing and showing the chaffer and sieve settings.
Typical sieve control systems are disclosed in Rowland-Hill et al. U.S. Pat. No. 4,466,231, issued Aug. 21, 1984 to Sperry Corporation; and Diekhans U.S. Pat. No. 6,205,384, issued Mar. 20, 2001 to Claas Selbstfahrende Erntemaschinen GmbH. U.S. Pat. No. 4,466,231 in particular discloses a method for automatic sieve and chaffer adjustment which ensures that the approach to the final position or setting is always made in the direction for opening the sieve, thereby allowing for compensation for play or backlash in the mechanical linkages of the system. However, to reduce the probability of the sieve or chaffer being damaged by crop material or foreign objects as it is moved to the setting, the sieve or chaffer is brought to a fully open position so as to pass any large and potentially damaging objects therethrough, then is moved in a closing direction to a more closed position past the desired setting by an amount corresponding to an anticipated amount of backlash or play in mechanical components of the system. Then, the sieve is opened by a corresponding amount to the desired setting. Possible shortcomings of this method of operation, however, include in the instance of a chaffer, the possible passage of larger pieces of plant material, such as stalk and stem fragments, into the openings of the chaffer so as to be caught or trapped therein or suspended therefrom, so as to decrease the capacity thereof as well as possibly also interfere with the operation of the sieve below, so as to reduce the capacity or efficiency of the cleaning system. In the instance of the lower finer sieve, if fully opened during the operation thereof when larger crop material is present thereon, the undesirable crop material can pass with the grain through the sieve so as to increase the percentage of impurities in the clean grain. This may be acceptable on an occasional basis. However, if it is desired to more frequently adjust the opening size of the finer sieve, for instance, such as for automatically maintaining a selected sieve opening size, more frequently fully opening the sieve may significantly increase the amount of unwanted crop material in the clean grain.
Accordingly what is sought is a system for automatically adjusting a sieve of an agricultural combine which overcomes many of the problems and shortcomings set forth above.
According to one aspect of the invention, a method of automatically controlling an opening size of a sieve of an agricultural combine is disclosed, which overcomes many of the problems and shortcomings identified above. The present method includes the steps of:
(a) storing a value for the opening size;
(b) determining an actual value for the opening size;
(c) comparing the actual value with the stored value, and,
(i) if the actual value is at least a predetermined amount greater than the stored value, then automatically closing the sieve until the actual value equals the stored value;
(ii) if the actual value is greater than the stored value by less than the predetermined amount, then automatically opening the sieve until the actual value is a predetermined amount greater than the stored value, then automatically closing the sieve until the actual value equals the stored value; and
(iii) if the actual value is less than the stored value, then automatically opening the sieve until the actual value is a predetermined amount greater than the stored value and then automatically closing the sieve until the actual value equals the stored value.
Preferably, the predetermined amounts are each an amount which correspond to or is only slightly or marginally greater than the amount of the anticipated tolerance stack-up for, or play in, the mechanical components of the system. The typical range of opening sizes for a particular sieve will equal several times the cumulative tolerance stack-up or play for the mechanical components of the system, which provides the advantage when the selected opening size is relatively small or in the lower portion of the range, that the sieve is only further opened by a relatively small amount, thereby limiting the number of larger pieces of plant material or contaminants that may be passed through or could become jammed or lodged in the sieve or chaffer, and the amount of smaller crop residue that would pass through the finer sieve with the clean grain. Also, because the sieve is only open a relatively small amount greater than the desired opening size, the adjustment can be completed in a time period shorter than required for opening the sieve from a smaller opening size to the fully opened position, closing the sieve to an opening size smaller than the desired size, then opening the sieve to the desired opening size, such as disclosed in U.S. Pat. No. 4,466,231.
As a preferred optional step, the sieve can be opened or closed to a commanded opening size, then a value for the commanded opening size stored for use as the stored value. Also preferably, during the prior step, the threshing mechanism or separator of the combine is not operating, such that any substantial flow of material therefrom to the sieve is absent. This allows the sieve to be moved, for instance, using an operator input device such as a push button or keypad, in an opening direction, a closing direction, or alternatively in both, for setting the sieve to a desired opening size without risk of becoming jammed with material therein or too large of material passing therethrough. Then, steps (a), (b) and (c) can be performed during the operation of the sieve when a flow of material from the separator is present, for making minor size adjustments for maintaining the sieve opening size at the desired value or setting.